[JdeBP]

Xe is conflating compilers and calling conventions a bit. The way that structure types are returned varies by calling convention, as indeed do a lot of other things. Mismatched calling conventions leads to problems.

But structure type return values are well specified for most calling conventions, and quite a number of compilers support explicitly specifying the calling convention for mixed-language or mixed-compiler situations.

* http://jdebp.uk./FGA/function-calling-conventions.html

[teddyh]

Many calling conventions apparently use a method for returning structs which is inherently non-thread-safe.

Also from that link:

> 32-bit cdecl calling convention

> For return values of structure or class type, there is wide incompatibility amongst compilers. Some make the return thread-safe, by breaking compatibility with the 16-bit cdecl calling convention. Some retain compatibility, at the expense of their 32-bit cdecl calling convention not being thread-safe. The ones that break compatibility don't all agree with one another on how to do so.